1. Field of the Invention
The invention relates to a fire alarm having a housing with a sensor, at least one radiation source, and an optical window. A reflector protection basket or ring is disposed above the optical window to protect the optical window and allow UV and IR radiation to pass through and reflect radiation from the housing interior.
The invention can be used wherever fire alarms are used to detect a fire and IR or UV radiation occurs, which is measured after it has passed through an optical window. Contamination of the optical window and function are monitored, and protection against mechanical damage of the window allows interference-free detection of fire phenomena.
2. The Prior Art
Fire alarms for detecting optical fire phenomena have been known for a long time. They generally consist of a housing, in which sensor elements and corresponding signal processing electronics are disposed. An optical window closes off the housing in the direction of the fire phenomenon to be detected. Radiation enters the housing through the optical window, and is detected by a sensor. However, the optical window can become dirty, thereby causing less radiation to enter the housing, and errors can occur in the detection. Furthermore, the result of the detection can be distorted by influences such as sunbeams, shadows, and the like. Furthermore, the optical window is exposed to mechanical influences that can lead to destruction or at least damage. In industrial areas or areas at risk of dust explosions, high demands are made on the seal and the mechanical strength of the housing and the optical entry window. A possible failure or disruption of the sensors and the signal processing electronics can also severely impair the reliability and availability of the fire detection. After installation and startup of a fire alarm, the alarm might have to be replaced after a certain period of time, for technical reasons or due to a change in the fire risk, by a fire alarm having the same construction, a fire alarm having different specification data, such as a different sensitivity class, for example, or even by a fire alarm that detects a different fire characteristic, for example heat or combustion gases. This requires a high level of installation effort. With known fire alarms, the entire alarm has to be removed and all of the cabling connections to the electrical power and the connection to a central fire alarm or a different reception device have to be disconnected. Subsequently, the new fire alarm has to be installed and connected with cables. This requires additional costs, and during the long time of refitting, no fire protection by means of automatic detection is guaranteed.
German Patent Application DE 42 40 395 A1 describes a detector for detecting electromagnetic radiation with a sensor element disposed in a housing that does not allow the radiation to pass through, under a cover disk that does allow the radiation to pass through. This element responds to electromagnetic radiation and generates an electrical output signal as a function of the radiation. The contamination of the cover disk is measured, in that the electromagnetic radiation of a radiation source is passed onto the cover disk, in other words the optical window, and measured in the interior of the detector as a measure of the contamination.
A similar device is described in U.S. Pat. No. 5,914,489, in which a light beam is passed from above, by a radiation source, onto the optical window, and is detected by a sensor below the optical window to the extent that the radiation penetrates the optical window, so that conclusions are possible with regard to the degree of contamination of the optical window.
In both solutions, the optical window is not protected against mechanical influences.
U.S. Pat. No. 5,257,013 describes a flame detector on the underside of which protection against mechanical stresses in the form of brackets or deflectors is disposed. However, the detector has no large-area optical window, and the mechanical protection does not monitor the degree of contamination of the entry window or to monitor the function of the sensors.
It is a further disadvantage of the available fire alarms that they each must be adjusted or converted in accordance with the fire event to be expected.
German Patent No. DE 203 06 590.5 describes a housing shell for a fire alarm that allows rapid conversion. An embodiment for a fire alarm is neither described nor indicated.
U.S. Pat. No. 4,547,673 describes a flame or smoke alarm having a radiation receiver element and maximally two radiation sources. This alarm has specially disposed reflectors. The reflective elements are optimized in such a manner that they influence a minimum of the surface of the entry window. It is disadvantageous that these reflectors do not offer sufficient mechanical protection, because of the geometric conditions (large optical window and small reflectors, in terms of area) and because of a lack of embodiments relating to the ability of the reflector material to withstand stress.
The recognition of fires by fire alarms can lead to false alarms if sunlight, artificial light, welding, heating devices, or other interference sources distort the result.
Furthermore, regulations provide that for fire alarms used in spaces at risk of explosion, the housing must be able to sustain great mechanical demands without damage, for example from strong impact or vibrations. The optical entry window must be sufficiently protected against these influences. In areas at risk of dust explosion, great demands are made on the chemical resistance of all the seal materials, as well as on the resistance resulting from ambient influences.
U.S. Pat. No. 3,952,196 A describes a UV fire alarm having a UV receiver element and UV transmitter, which alarm has a crosspiece with reflective elements above the optical window. The crosspiece and the reflective elements are only provided for contamination monitoring of the optical window. Because of the geometric conditions (large optical window and small crosspiece, in terms of area), this reflector does not guarantee sufficient mechanical protection. Also, no function monitoring of the sensors and of the signal processing electronics is provided. Furthermore, the reflector cannot be easily replaced. Since the holder of the reflector holds the optical window at the same time, replacement of the reflector is complicated. Without this part, however, the alarm is unable to function, since the optical window otherwise does not have any hold in the present method of construction.